Charles M. Kozierok The TCP-IP Guide

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☯ NNTP Client-Server Communication Process: News Posting and Access .........1505

☯ NNTP Commands......................................................................................................1509

☯ NNTP Command Extensions....................................................................................1512

☯ NNTP Status Responses and Response Codes.....................................................1517

☯ TCP/IP World Wide Web (WWW, "The Web") and the Hypertext

Transfer Protocol (HTTP).............................................................................1522

☯ TCP/IP World Wide Web and Hypertext Overview and Concepts..................1523

☯ World Wide Web and Hypertext Overview and History .........................................1523

☯ World Wide Web System Concepts and Components ..........................................1525

☯ World Wide Web Media and the Hypertext Markup Language (HTML) ................1528

☯ World Wide Web Addressing: HTTP Uniform Resource Locators (URLs) ..........1533

☯ TCP/IP Hypertext Transfer Protocol (HTTP) ....................................................1536

☯ HTTP Overview, History, Versions and Standards ................................................1537

☯ HTTP General Operation and Connections ............................................................1540

☯ HTTP Operational Model and Client/Server Communication .........................1540

☯ HTTP Transitory and Persistent Connections and Pipelining........................1543

☯ HTTP Persistent Connection Establishment, Management and

Termination .........................................................................................................1545

☯ HTTP Messages, Message Formats, Methods and Status Codes ........................1548

☯ HTTP Generic Message Format.........................................................................1548

☯ HTTP Request Message Format........................................................................1550

☯ HTTP Response Message Format.....................................................................1553

☯ HTTP Methods.....................................................................................................1555

☯ HTTP Status Code Format, Status Codes and Reason Phrases....................1559

☯ HTTP Message Headers ...........................................................................................1565

☯ HTTP General Headers.......................................................................................1565

☯ HTTP Request Headers ......................................................................................1569

☯ HTTP Response Headers ...................................................................................1573

☯ HTTP Entity Headers ..........................................................................................1575

☯ HTTP Entities, Transfers, Coding Methods and Content Management ...............1578

☯ HTTP Entities and Internet Media Types ..........................................................1578

☯ HTTP Data Transfer, Content Encodings and Transfer Encodings ...............1580

☯ HTTP Data Length Issues, "Chunked" Transfers and Message Trailers.......1583

☯ HTTP Content Negotiation and "Quality Values" ............................................1587

☯ HTTP Features, Capabilities and Issues .................................................................1590

☯ HTTP Caching Features and Issues..................................................................1590

☯ HTTP Proxy Servers and Proxying ...................................................................1594

☯ HTTP Security and Privacy ................................................................................1597

☯ HTTP State Management Using "Cookies" ......................................................1599

☯ Gopher Protocol (Gopher) ...........................................................................1603

☯ TCP/IP Interactive and Remote Application Protocols ........................1607

☯ Telnet Protocol..............................................................................................1608

☯ Telnet Overview, History and Standards .........................................................1608

☯ Telnet Connections and Client/Server Operation ...........................................1611

☯ Telnet Communications Model and the Network Virtual Terminal (NVT) .....1613

☯ Telnet Protocol Commands...............................................................................1617

☯ Telnet Interrupt Handling Using Out-Of-Band Signaling: The Telnet

Synch Function ..................................................................................................1620

☯ Telnet Options and Option Negotiation ...........................................................1622

☯ Berkeley Remote ("r") Commands..............................................................1628

☯ Berkeley Remote Login (rlogin)........................................................................1628

☯ Berkeley Remote Shell (rsh)..............................................................................1630

☯ Other Berkeley Remote ("r") Commands (rcp, ruptime, rwho) ......................1631

☯

Internet Relay Chat Protocol (IRC)..............................................................1633

☯ TCP/IP Administration and Troubleshooting Utilities and Protocols.1636

☯ TCP/IP Host Name Utility (hostname).........................................................1637

☯ TCP/IP Communication Verification Utility (ping/ping6)...........................1638

☯ TCP/IP Route Tracing Utility (traceroute/tracert/traceroute6) ..................1643

☯ TCP/IP Address Resolution Protocol Utility (arp)......................................1648

☯ TCP/IP DNS Name Resolution and Information Lookup Utilities

(nslookup, host and dig) ..............................................................................1649

☯ TCP/IP DNS Registry Database Lookup Utility (whois/nicname) .............1655

☯ TCP/IP Network Status Utility (netstat).......................................................1657

☯ TCP/IP Configuration Utilities (ipconfig, winipcfg and ifconfig) ..............1664

☯ Miscellaneous TCP/IP Troubleshooting Protocols: Echo,

Discard, Character Generator, Quote Of The Day, Active Users,

Daytime, Time ...............................................................................................1670

List of Figures

Figure 2: Packet Switching ............................................................................................67

Figure 1: Circuit Switching ............................................................................................67

Figure 3: Network Message Formatting........................................................................74

Figure 4: Unicast, Multicast and Broadcast Message Addressing and

Transmission.......................................................................................................76

Figure 5: Peer-to-Peer Networking................................................................................78

Figure 6: Client/Server Networking ...............................................................................79

Figure 7: Internet Standards Organizations...............................................................111

Figure 8: Binary Information Representations and Terms .......................................122

Figure 9: Binary, Octal and Hexadecimal Number Representations .......................125

Figure 10: Clearing Bits Using an AND Bit Mask.......................................................137

Figure 11: OSI Reference Model Layers .....................................................................150

Figure 12: OSI Reference Model Layer Relationships and Terminology.................152

Figure 13: OSI Reference Model Interfaces for Vertical Communication................155

Figure 14: OSI Reference Model Protocols: Horizontal Communication ................158

Figure 15: OSI Reference Model Data Encapsulation ...............................................159

Figure 16: OSI Reference Model PDU and SDU Encapsulation................................161

Figure 17: Message Routing in the OSI Reference Model ........................................164

Figure 18: OSI Reference Model Mnemonics .............................................................182

Figure 19: TCP/IP Client/Server Operation .................................................................192

Figure 20: OSI Reference Model and TCP/IP Model Layers......................................195

Figure 21: TCP/IP Protocols.........................................................................................198

Figure 22: Operation of the Serial Line Internet Protocol (SLIP)..............................211

Figure 23: PPP Location in TCP/IP Architecture........................................................216

Figure 24: Overview of PPP Operation .......................................................................219

Figure 25: PPP Phases.................................................................................................221

Figure 26: PPP Link Control Protocol (LCP) Message Exchanges ..........................229

Figure 27: PPP LCP Link Configuration Process ......................................................231

Figure 28: PPP IP Control Protocol (IPCP) Message Exchanges.............................235

Figure 29: PPP Password Authentication Protocol (PAP) Authentication..............237

Figure 30: PPP Challenge Handshake Authentication Protocol (CHAP)

Authentication ...................................................................................................238

Figure 31: Multilink PPP Architecture.........................................................................249

Figure 32: PPP General Frame Format .......................................................................256

Figure 33: Sample PPP Data Frame ............................................................................256

Figure 34: PPP Control Message Format ...................................................................261

Figure 35: PPP Control Message Carrying Options ..................................................263

Figure 36: PPP Control Message Option Format.......................................................264

Figure 37: PPP PAP Authenticate-Request Frame Format .......................................269

Figure 38: PPP PAP Authenticate-Ack and Authenticate-Nak Frame Format.........269

Figure 39: PPP CHAP Challenge and Response Frame Format...............................271

Figure 40: PPP CHAP Success and Failure Frame Format.......................................271

Figure 41: PPP Multilink Protocol Long Fragment Frame Format ...........................273

Figure 42: PPP Multilink Protocol Short Fragment Frame Format...........................274

Figure 43: PPP Multilink Protocol (MP) Fragmentation Demonstration ..................276

Figure 44: Why Address Resolution Is Necessary ....................................................281

Figure 45: Address Resolution Through Direct Mapping .........................................283

Figure 46: Address Resolution Problems With Large Hardware Address Size......284

Figure 47: Dynamic Address Resolution....................................................................286

Figure 48: Address Resolution Protocol (ARP) Transaction Process.....................292

Figure 49: Address Resolution Protocol (ARP) Message Format............................296

Figure 50: ARP Proxy Operation .................................................................................300

Figure 51: Mapping of Multicast IP Addresses to IEEE 802 Multicast MAC

Addresses..........................................................................................................302

Figure 52: Operation of the Reverse Address Resolution Protocol (RARP)...........306

Figure 53: Reverse Address Resolution Protocol (RARP) Operation......................307

Figure 54: The Main Function of IP: Internetwork Datagram Delivery.....................312

Figure 55: IP Interfaces for Common Network Devices ............................................321

Figure 56: IP Address Binary, Hexadecimal and Dotted Decimal

Representations ................................................................................................324

Figure 57: Basic IP Address Division: Network ID and Host ID ...............................326

Figure 58: Mid-Octet IP Address Division ..................................................................327

Figure 59: Multihomed Devices On An IP Internetwork ............................................331

Figure 60: Division of IPv4 Address Space Into Classes..........................................336

Figure 61: Class Determination Algorithm for “Classful” IP Addresses.................338

Figure 62: IP Address Class Bit Assignments and Network/Host ID Sizes.............341

Figure 63: IP Multicast Address Ranges and Uses ...................................................350

Figure 64: The Main Problem With “Classful” Addressing.......................................353

Figure 65: Subnetting A Class B Network ..................................................................358

Figure 66: Determining the Subnet Mask of a Subnetted Network ..........................361

Figure 67: Determining the Subnet ID of an IP Address Through Subnet

Masking..............................................................................................................362

Figure 68: Default Subnet Masks for Class A, Class B and Class C Networks ......365

Figure 69: Custom Subnet Masks for Class C Networks ..........................................369

Figure 70: Class C (/24) Network Split Into Eight Conventional Subnets................378

Figure 71: Class C (/24) Network Split Using Variable Length Subnet Masking

(VLSM)................................................................................................................379

Figure 72: Variable Length Subnet Masking (VLSM) Example .................................381

Figure 73: Subnetting Design Trade-Off For Class C Networks...............................385

Figure 74: Example Class C Subnetting: An “Easy Decision” .................................386

Figure 75: Example Class B Subnetting: A More Difficult Decision ........................387

Figure 76: Determining The Custom Subnet Mask for A Class C Network .............389

Figure 77: Determining The Custom Subnet Mask for A Class B Network .............390

Figure 78: Determining Subnet Addresses For A Class C Network ........................393

Figure 79: Determining Subnet Addresses For A Class B Network ........................395

Figure 80: Determining Host Addresses For A Class C Network.............................399

Figure 81: Classless Addressing (CIDR) Solves The “Granularity Problem” .........405

Figure 82: CIDR (“Slash”) Notation and Its Subnet Mask Equivalent......................407

Figure 83: Example Hierarchical Division Of A /15 CIDR Address Block................412

Figure 84: Hierarchical Address Division Using Classless Addressing (CIDR) .....413

Figure 85: IP Datagram Encapsulation .......................................................................418

Figure 86: Internet Protocol Version 4 (IPv4) Datagram Format ..............................423

Figure 87: Internet Protocol Version 4 (IPv4) Option Format ...................................427

Figure 88: IP Maximum Transmission Unit (MTU) and Fragmentation....................432

Figure 89: IPv4 Datagram Fragmentation...................................................................433

Figure 90: IPv4 Datagram Fragmentation Process....................................................436

Figure 91: Direct and Indirect (Routed) Delivery of IP Datagrams ...........................442

Figure 92: IP Datagram Next-Hop Routing .................................................................446

Figure 93: IP Routing and Routing Tables .................................................................448

Figure 94: A (Poor) Representation of Relative IPv4 and IPv6 Address

Space Sizes .......................................................................................................465

Figure 95: Binary, Decimal and Hexadecimal Representations of IPv6

Addresses..........................................................................................................467

Figure 96: IPv6 Global Unicast Address Format........................................................474

Figure 97: Example IPv6 Unicast Routing Prefix Structure ......................................478

Figure 98: Converting IEEE 802 MAC Addresses To IPv6 Modified EUI-64

Identifiers ...........................................................................................................481

Figure 99: IPv4-Compatible Embedded IPv6 Address Representation ...................485

Figure 100: IPv4-Mapped Embedded IPv6 Address Representation .......................485

Figure 101: IPv6 Multicast Address Format ...............................................................488

Figure 102: IPv6 Multicast Scope................................................................................489

Figure 103: IPv6 Solicited Node Address Calculation...............................................490

Figure 104: IPv6 General Datagram Structure ...........................................................497

Figure 105: IPv6 Main Header Format.........................................................................499

Figure 106: IPv6 Extension Header Linking Using the Next Header Field ..............502

Figure 107: IPv6 Routing Extension Header Format .................................................505

Figure 108: IPv6 Fragment Extension Header Format ..............................................506

Figure 109: IPv6 Hop-By-Hop Options and Destination Options Header

Formats ..............................................................................................................509

Figure 110: IPv6 Datagram Fragmentation.................................................................515

Figure 111: IP Network Address Translation (NAT) Terminology ............................526

Figure 112: Operation Of Unidirectional (Traditional/Outbound) NAT ....................530

Figure 113: Operation Of Bidirectional (Two-Way/Inbound) NAT ............................534

Figure 114: Operation Of Port-Based (“Overloaded”) NAT ......................................538

Figure 115: Operation Of “Overlapping” NAT / “Twice NAT”...................................542

Figure 116: Overview of IPSec Protocols and Components.....................................549

Figure 117: IPSec “Bump In The Stack” (BITS) Architecture ...................................552

Figure 118: IPSec “Bump In The Wire” (BITW) Architecture ....................................553

Figure 119: IPSec Transport Mode Operation............................................................554

Figure 120: IPSec Tunnel Mode Operation.................................................................556

Figure 121: IPv6 Datagram Format With IPSec Authentication Header (AH) ..........561

Figure 122: IPv4 Datagram Format With IPSec Authentication Header (AH) ..........562

Figure 123: IPSec Authentication Header (AH) Format.............................................563

Figure 124: IPv6 Datagram Format With IPSec Encapsulating Security

Payload (ESP)....................................................................................................566

Figure 125: IPv4 Datagram Format With IPSec Encapsulating Security

Payload (ESP)....................................................................................................567

Figure 126: IPSec Encapsulating Security Payload (ESP) Format...........................569

Figure 127: The Main Problem With Mobile Devices on IP Internetworks...............574

Figure 128: General Operation of the Mobile IP Protocol .........................................578

Figure 129: Mobile IP Operation With A Foreign Agent “Care-Of” Address ...........582

Figure 130: Mobile IP Mobility Agent Advertisement Extension Format.................587

Figure 131: Mobile IP Prefix-Lengths Extension Format ..........................................588

Figure 132: Mobile IP Registration Request Message Format .................................591

Figure 133: Mobile IP Registration Reply Message Format......................................594

Figure 134: Mobile IP Encapsulation and Tunneling.................................................596

Figure 135: ARP Proxying By Mobile IP Home Agent ...............................................599

Figure 136: A Mobile IP Inefficiency “Worst Case Scenario” ...................................601

Figure 137: ICMP General Operation ..........................................................................609

Figure 138: ICMP Common Message Format.............................................................617

Figure 139: ICMPv4 Destination Unreachable Message Format ..............................621

Figure 140: ICMPv4 Source Quench Message Format..............................................625

Figure 141: Expiration of an IP Datagram and Time Exceeded Message

Generation .........................................................................................................627

Figure 142: ICMPv4 Time Exceeded Message Format ..............................................628

Figure 143: Host Redirection Using an ICMP Redirect Message .............................630

Figure 144: ICMPv4 Redirect Message Format..........................................................631

Figure 145: ICMPv4 Parameter Problem Message Format .......................................634

Figure 146: ICMPv4 Echo and Echo Reply Message Format....................................637

Figure 147: ICMPv4 Timestamp and Timestamp Reply Message Format ...............640

Figure 148: ICMPv4 Router Advertisement Message Format...................................642

Figure 149: ICMPv4 Router Solicitation Message Format ........................................643

Figure 150: ICMPv4 Address Mask Request and Address Mask Reply

Message Format................................................................................................645

Figure 151: ICMPv4 Traceroute Message Format......................................................647

Figure 152: ICMPv6 Destination Unreachable Message Format ..............................650

Figure 153: ICMPv6 Packet Too Big Message Format ..............................................653

Figure 154: An Example of A Router Loop.................................................................655

Figure 155: ICMPv6 Time Exceeded Message Format ..............................................656

Figure 156: ICMPv6 Parameter Problem Message Format .......................................658

Figure 157: ICMPv6 Echo Request and Echo Reply Message Format ....................662

Figure 158: ICMPv6 Router Advertisement Message Format...................................665

Figure 159: ICMPv6 Router Solicitation Message Format ........................................666

Figure 160: ICMPv6 Neighbor Advertisement Message Format...............................669

Figure 161: ICMPv6 Neighbor Solicitation Message Format ....................................670

Figure 162: ICMPv6 Redirect Message Format..........................................................673

Figure 163: ICMPv6 Router Renumbering Message Format.....................................676

Figure 165: ICMPv6 Target Link-Layer Address Option Format ..............................678

Figure 164: ICMPv6 Source Link-Layer Address Option Format .............................678

Figure 166: ICMPv6 Prefix Information Option Format .............................................680

Figure 167: ICMPv6 Redirected Header Option Format ............................................681

Figure 168: ICMPv6 MTU Option Format ....................................................................682

Figure 169: Neighbor Discovery Protocol (ND) Functional Groups and

Functions ...........................................................................................................686

Figure 170: ND Host Redirection Using an ICMPv6 Redirect Message ...................694

Figure 171: TCP/IP Autonomous System (AS) Routing Architecture ......................700

Figure 172: Example RIP Autonomous System .........................................................709

Figure 173: Propagation of Network Routing Information Using RIP......................710

Figure 174: The RIP “Counting To Infinity” Problem ................................................716

Figure 175: RIP Problem Solving Using Split Horizon With Poisoned

Reverse ..............................................................................................................720

Figure 176: RIP Version 1 (RIP-1) Message Format...................................................725

Figure 177: RIP Version 2 (RIP-2) Message Format...................................................729

Figure 178: RIPng Message Format............................................................................732

Figure 179: Example OSPF Autonomous System .....................................................736

Figure 180: Example OSPF Hierarchical Topology Autonomous System ..............740

Figure 181: Example OSPF Autonomous System With Costs .................................743

Figure 182: OSPF Route Determination Using The Shortest Path First

Algorithm ...........................................................................................................744

Figure 183: OSPF Calculated Shortest Path First Tree.............................................745

Figure 184: OSPF Common Header Format...............................................................749

Figure 185: OSPF Hello Message Format...................................................................750

Figure 186: OSPF Database Description Message Format.......................................752

Figure 187: OSPF Link State Request Message Format ...........................................753

Figure 189: OSPF Link State Acknowledgment Message Format............................754

Figure 188: OSPF Link State Update Message Format .............................................754

Figure 190: OSPF Link State Advertisement Header Format ...................................756

Figure 191: BGP Example Topology and Designations ............................................773

Figure 192: BGP General Message Format ................................................................787

Figure 193: BGP Open Message Format ....................................................................790

Figure 194: BGP Update Message Format .................................................................795

Figure 195: BGP Keepalive Message Format.............................................................797

Figure 196: BGP Notification Message Format..........................................................799

Figure 197: Process Multiplexing and Demultiplexing In TCP/IP.............................812

Figure 198: TCP/IP Process Multiplexing/Demultiplexing Using TCP/UDP

Ports ...................................................................................................................815

Figure 199: TCP/IP Client/Server Application Port Mechanics.................................821

Figure 201: UDP Pseudo Header Format....................................................................831

Figure 200: UDP Message Format...............................................................................831

Figure 202: TCP Data Stream Processing and Segment Packaging........................847

Figure 203: Operation Of An Unreliable Protocol......................................................850

Figure 204: Basic Reliability: Positive Acknowledgment With

Retransmission (PAR) ......................................................................................851

Figure 205: Enhanced Positive Acknowledgment With Retransmission (PAR) .....853

Figure 206: Conceptual Division of TCP Transmission Stream Into Categories....855

Figure 207: TCP Transmission Stream Categories and Send Window

Terminology.......................................................................................................856

Figure 208: TCP Stream Categories and Window After Sending Usable

Window Bytes....................................................................................................857

Figure 209: Sliding The TCP Send Window................................................................858

Figure 210: The TCP Finite State Machine (FSM) ......................................................868

Figure 211: TCP “Three-Way Handshake” Connection Establishment

Procedure ..........................................................................................................874

Figure 212: TCP Simultaneous Open Connection Establishment Procedure.........875

Figure 213: TCP Sequence Number Synchronization...............................................878

Figure 214: TCP Connection Termination Procedure ...............................................885

Figure 215: TCP Simultaneous Connection Termination Procedure.......................888

Figure 216: TCP Segment Format ...............................................................................893

Figure 217: TCP “Pseudo Header” For Checksum Calculation ...............................896

Figure 218: TCP Header Checksum Calculation........................................................897

Figure 219: TCP Transmission Categories, Send Window and Pointers ................903

Figure 220: TCP Receive Categories and Pointers....................................................904

Figure 221: TCP Transaction Example Showing Server’s Send Pointers ...............910

Figure 222: TCP Transaction Example Showing Client’s Send Pointers ................911

Figure 223: TCP Transaction Example With Retransmission...................................920

Figure 224: TCP “Aggressive” Retransmission Example.........................................924

Figure 225: TCP Retransmission With Selective Acknowledgment (SACK)...........926

Figure 226: TCP Window Size Adjustments and Flow Control ................................931

Figure 227: The Problem With “Shrinking” The TCP Window..................................934

Figure 228: TCP “Silly Window Syndrome” ...............................................................938

Figure 229: Internetwork Access Without A Name System ......................................950

Figure 230: Internetwork Access With A Name System............................................951

Figure 231: Name System Functions..........................................................................953

Figure 232: Flat Name Architecture (Flat Name Space) ............................................955

Figure 233: Hierarchical Name Architecture (Structured Name Space) ..................956

Figure 234: DNS Functions ..........................................................................................978

Figure 235: Example of a Global Hierarchical Domain Architecture .......................982

Figure 236: DNS Name Space Tree and Domain-Related Terminology...................985

Figure 237: DNS Name Space “Family Tree” .............................................................986

Figure 238: DNS Labels and Domain Name Construction ........................................989

Figure 239: Internet DNS Organizational (Generic) Top-Level Domains

(TLDs).................................................................................................................998

Figure 240: DNS Zones Of Authority.........................................................................1009

Figure 241: DNS Resource Record Master File and Binary Field Formats ...........1018

Figure 242: Geographic Locations of Internet DNS Root Name Servers ..............1029

Figure 243: Iterative DNS Name Resolution.............................................................1041

Figure 244: Recursive DNS Name Resolution..........................................................1042

Figure 245: Example Of The DNS Name Resolution Process.................................1048

Figure 246: The DNS IN-ADDR.ARPA Reverse Name Resolution Hierarchy ........1051

Figure 247: DNS General Message Format ..............................................................1059

Figure 248: DNS Message Header Format................................................................1064

Figure 249: DNS Message Question Section Format ..............................................1065

Figure 250: DNS Common Resource Record Format..............................................1067

Figure 251: DNS Start Of Authority Resource Record Data Format ......................1070

Figure 252: DNS Standard Name Notation ...............................................................1072

Figure 253: NFS Architectural Components ............................................................1088

Figure 254: General Operation Of the Boot Protocol ..............................................1111

Figure 255: Boot Protocol Operation........................................................................1113

Figure 256: BOOTP Message Format........................................................................1118

Figure 257: BOOTP Vendor-Specific Area Format Showing Vendor

Information Fields ...........................................................................................1120

Figure 258: BOOTP Operation Using A Relay Agent...............................................1124

Figure 259: DHCP “Life Cycle” Example ..................................................................1139

Figure 260: DHCP Scope............................................................................................1141

Figure 261: DHCP Multi-Server Non-Overlapping Scopes......................................1142

Figure 262: DHCP Client Finite State Machine.........................................................1152

Figure 263: DHCP Lease Allocation Process ...........................................................1154

Figure 264: DHCP Lease Reallocation Process .......................................................1159

Figure 265: DHCP Lease Renewal and Rebinding Processes................................1163

Figure 266: DHCP Parameter Configuration Process .............................................1167

Figure 267: DHCP Message Format ..........................................................................1176

Figure 268: DHCP Options Field Format ..................................................................1178

Figure 269: DHCP Automatic Private IP Addressing (APIPA) ................................1197

Figure 270: SNMP Operational Model .......................................................................1211

Figure 271: Components of the TCP/IP Internet Standard Management

Framework .......................................................................................................1213

Figure 272: SNMP Management Information Base (MIB) ........................................1227

Figure 273: Global Object Name Hierarchy and SNMP MIB Hierarchies ...............1233

Figure 274: SNMP Information Poll Process............................................................1246

Figure 275: SNMP Object Modification Process ......................................................1249

Figure 276: SNMP General Message Format............................................................1260

Figure 277: SNMP Version 1 (SNMPv1) General Message Format.........................1262

Figure 278: SNMP Version 1 (SNMPv1) Common PDU Format ..............................1264

Figure 279: SNMP Version 1 (SNMPv1) Trap-PDU Format......................................1265

Figure 280: SNMP Version 2 (SNMPv2p) General Message Format ......................1267

Figure 281: Community-Based SNMP Version 2 (SNMPv2c) General

Message Format..............................................................................................1268

Figure 282: User-Based SNMP Version 2 (SNMPv2u) General Message

Format ..............................................................................................................1270

Figure 283: SNMP Version 2 (SNMPv2) Common PDU Format ..............................1273

Figure 284: SNMP Version 2 (SNMPv2) GetBulkRequest-PDU Format .................1274

Figure 285: SNMP Version 3 (SNMPv3) General Message Format.........................1276

Figure 286: SNMP Remote Network Monitoring (RMON) MIB Hierarchy...............1280

Figure 287: Example Uniform Resource Locator (URL)..........................................1290

Figure 288: File Transfer Protocol (FTP) Operational Model ..................................1321

Figure 289: FTP Connection Establishment and User Authentication ..................1324

Figure 290: FTP Active Data Connection..................................................................1327

Figure 291: FTP Passive Data Connection...............................................................1328

Figure 292: FTP Reply Code Format .........................................................................1341

Figure 293: TFTP Read Process................................................................................1358

Figure 294: TFTP Write Process................................................................................1360

Figure 295: TFTP Read Process With Option Negotiation......................................1362

Figure 296: TFTP Read Request / Write Request Message Format .......................1365

Figure 298: TFTP Acknowledgment Message Format.............................................1366

Figure 297: TFTP Data Message Format...................................................................1366

Figure 299: TFTP Error Message Format..................................................................1367

Figure 300: TFTP Option Acknowledgment Message Format ................................1368

Figure 301: Electronic Mail (E-Mail) Communication Model...................................1377

Figure 302: MIME Multipart Message Structure .......................................................1414

Figure 303: MIME Base64 Encoding .........................................................................1419

Figure 304: SMTP Transaction Session Establishment and Termination .............1428

Figure 305: SMTP Mail Transaction Process ...........................................................1432

Figure 306: Post Office Protocol (POP3) Finite State Machine ..............................1454

Figure 307: Post Office Protocol (POP3) User Authentication Process ................1455

Figure 308: Post Office Protocol (POP3) Mail Exchange Process .........................1459

Figure 309: Internet Message Access Protocol (IMAP) Finite State Machine .......1467

Figure 310: Usenet (Network News) Communication Model ..................................1489

Figure 311: Usenet Newsgroup Hierarchies.............................................................1493

Figure 312: NNTP Article Propagation Using The “Push” Model...........................1504

Figure 313: NNTP Full Newsgroup Retrieval Process.............................................1507

Figure 314: Major Functional Components of the World Wide Web......................1526

Figure 315: HTTP Client/Server Communication .....................................................1541

Figure 316: HTTP Request/Response Chain Using Intermediaries .......................1542

Figure 317: HTTP Request Message Format............................................................1551

Figure 318: HTTP Response Message Format.........................................................1554

Figure 319: Impact of Caching on HTTP Request/Response Chain ......................1591

Figure 320: Telnet Communication and the Network Virtual Terminal (NVT) .......1615

Figure 321: Operation of the traceroute/tracert Utility ............................................1645

Figure 322: Windows 95/98/ME winipcfg Utility .......................................................1669